The invention relates to a generator for power generation for high-frequency surgery. In high-frequency surgery, human or animal body tissue is cut or coagulated by means of an electric current. High-frequency surgery is usable with extreme advantage, particularly with endoscopic operating techniques.
1. Field of the Invention
It is the purpose of high-frequency surgical generators to provide electrical energy for high-frequency surgery in such manner that a desired operation result is obtained. In order to minimize muscle and nerve irritation, high-frequency surgical generators supply high-frequency energy in a frequency range above 300 kHz. This high-frequency energy is usually introduced into tissue by means of an electrode. Strong heating of the tissue surrounding the electrode occurs at the site of introduction. If high energy is supplied within a short period of time, this results in a vaporization of cell fluid and a bursting of cells, so that the group of cells around the electrode disintegrates. The electrode can move almost freely through the tissue. If less energy is supplied for a long period of time, this results in a coagulation of the tissue, i.e. to congealing of protein. In this case, the cells die off and become a viscous mass.
As far as the introduction of high-frequency energy is concerned, basically a distinction is made between two arrangements.
In a monopolar arrangement, a cutting or coagulating electrode having a small surface for introducing current is disposed at the site of operation, and a “neutral” electrode of large surface for conducting current away is disposed at a different site on the body of a patient. Here the electrode surface is dimensioned to be large enough for no appreciable heat to be developed at the electrode.
A bipolar arrangement comprises a divided electrode with which an introduction of current and a conducting away of current occur at the site of the operation.
Dosing of the energy is of great importance, because this directly affects the result of the operation. If the generator supplies too little energy, then no cutting is possible, and if too much energy is supplied, then the cut edges are strongly coagulated, which in turn leads to difficult healing or increased risk of infection.
Therefore, it is the aim to introduce into the body as little energy as possible for a pure cutting process, and the minimum amount of energy needed for coagulation for a combined cutting and coagulating process.
2. Description of the Prior Art
For minimization of this energy, the U.S. Pat. No. 4,114,623 discloses a method for regulating the generator current by observations of the electric arc appearing during cutting.
Here a start of cutting, or a transition to a different kind of tissue having different electrical properties, presents a special problem. Because a transition to a different kind of tissue involves almost the same problem as is set by a start of cutting, reference will be made in the following to only the start of cutting.
If cutting is started with too high power, an undesired coagulation will already occur at the site of cutting. In order to minimize this coagulation, DE 38 15 835 A1 proposes that the generator output voltage be limited. This prevents a first cut from being made with too high generator power. If, instead of this, a first cut is made with too low power, this will lead to no cutting process being performed by penetration of the electrode into the tissue, but rather to an undesired coagulation of the tissue surface. This will also make a further first cut more difficult. In order to ensure a safe first cut without dependence on the tissue, DE 41 35 184 A1 proposes that an increased generator power be supplied at the start of making a first cut. This increased emission of power can then be lowered to the value normally needed for cutting when an electric arc is detected.
Both measures proposed here for optimizing a start of cutting exclude each other. Thus, one the one hand, to avoid a coagulation by too high a generator power, the generator power can be limited, which however can lead to a coagulation in case no first cut is made. On the other hand, a first cut can be made with increased power, whilst accepting an occurrence of coagulation.